The sexual imperative. Part 4, From conception to birth.

The Sexual Imperative series explores the reasons for sexual and asexual reproduction in the insect, animal and human worlds. This episode looks at conception and birth. The voiceover explains the importance of water in conception; even humans are conceived in water. Coral, Siamese fighting fish, Euroepan bitterlings and Jamaican frogs reproduce using the water in an obvious way, laying eggs and fertilising them. Animals that conceive internally are also shown, including bird-eating spiders, lovebirds, Australian grey-headed bats, porcupines, mice, and Mediterranean cuttlefish. Males that act possessively over their females or eggs are shown, including damsel flies, giant waterbugs and jacana birds. Pouched mammals are shown, including wallabees. Animals whose young are born fully capable are shown, including chameleons and wildebeast, and those whose young are born more helpless are shown, including tsetse flies and fruit bats.